The present invention relates to gas turbine engines having convergent/divergent nozzles, and more particularly to a nozzle divergent section cooling arrangement.
An exhaust nozzle optimizes the thrust produced within a gas turbine engine. In augmented gas turbine engines, convergent/divergent (CID) nozzles provide a multitude of nozzle positions. Flaps circumferentially distributed aft of the augmentor or exhaust duct form the convergent and divergent sections for which the nozzle is named. Flap seals disposed between adjacent flaps minimize gas leakage between flaps in both sections. The convergent section is pivotally connected to the augmentor or exhaust duct and to the divergent section. The divergent section is pivotally connected to the convergent section and to an external fairing positioned radially outboard of the divergent section. The opposite end of the external fairing is pivotally attached to a static outer casing which surrounds a portion of the nozzle. Together, the outer casing, the convergent and divergent sections, and the external fairing form a nozzle plenum.
Because of the high temperature of the core gas exiting the turbine and augmentor, nozzles are cooled with air bled off of the fan at a lower temperature and a higher pressure than that of the core gas flow passing through the nozzle. Cooling air enters the core gas path within the augmentor or exhaust duct via cooling holes in the augmentor or exhaust duct liner and subsequently passes into the nozzle as a layer of cooling air traveling along the surface of the nozzle flaps and flap seals. Cooling air within the nozzle plenum cools the opposite side of the flaps and flap seals.
Various amounts of cooling air are required to properly cool the divergent section at various operating conditions. In conventional nozzles, airflow is typically established based on the maximum airflow that would be required under the most adverse condition. This forced airflow continues to operate at other operating conditions where the full amount may not be required for cooling. The diversion of excess cooling air from the core airflow decreases the efficiency of the engine.
Accordingly, it is desirable to provide adequate cooling for the divergent sections while efficiently utilizing the cooling air.